1. Field of the Invention
This invention relates to self-developing photographic film units and to the manufacture of such film units.
2. Description of the Prior Art
Self-developing photographic film units are known which include an integral imaging receiver (IIR) sheet and a second sheet, sometimes termed a cover sheet. Between the IIR sheet and the cover sheet are a mask sheet and spacer rails. A container of processing composition and a trap, including a trap spacer, are at opposite margins of the film unit. Such film units are exposed through the cover sheet and the visible image created by processing initiated by spreading processing composition, from the container, throughout the film unit, is viewed from the opposite side, i.e. by looking at the IIR sheet.
Text No. 17622 published in the December 1978 edition of the journal Research Disclosure, published by Industrial Opportunities Ltd. of Homewell, Havant, England, describes a self-processing photographic film unit which permits but does not require the removal of expended processing materials. That text describes the provision of a stripping layer in the IIR sheet between the photosensitive layers and the image-receiving layer. In the structure illustrated in and described with reference to FIG. 5 of that text there is a score line (21) which allows an unwanted marginal portion of the receiver sheet to be separated from the wanted image-bearing portion--the unwanted portion remaining with the expended processing materials.
It is known to make film units from continuous webs by a production method which involves the application of heat energy to activate heat activatable adhesives. It was found that if the receiver sheet web is slit into two discrete part webs prior to the heat sealing of the receiver sheet web to the mask web, differential stretching created a problem in the form of an increasingly large loop in one of the part webs between the slitting position and the heat-sealing position. Also there were problems in keeping the two part webs in the desired mutually abutting relationship.
It is an object of the present invention to provide a film unit and a method of production of a film unit in which said problems are overcome.